Fludrocortisone: what it treats, how to take it, side effects
Last updated September 3, 2026.
Fludrocortisone is a corticosteroid - it helps the body hold onto sodium and fluid instead of losing them in the urine. For Addison's disease and the salt-losing syndromes, it replaces what the adrenals no longer do.
What does it treat?
Addison's disease and syndromes where excessive sodium is lost in the urine - and other uses your doctor can explain.
How do you take it?
Once daily, exactly as directed - same time each morning. Never stop suddenly: the body leans on it - the taper is the doctor's schedule. Diet is part of the prescription: your doctor may set low-sodium, low-salt, potassium-rich, or high-protein instructions - follow them. Salt tablets sometimes ride alongside. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: upset stomach, vomiting, headache, dizziness, insomnia, restlessness, mood changes like depression or anxiety, acne, increased sweating.
- Serious - call your doctor immediately: skin rash; swelling of the face, lower legs, or ankles; vision problems; a cold or infection that will not clear; muscle weakness; black or tarry stools; unusual weight gain; and severe stomach pain.
Who should not take it?
Infections get flagged - steroids quiet the immune system: a lingering cold is a report, not a shrug. High blood pressure, heart, kidney, liver, thyroid, eye, and stomach conditions all shape the dose. Diabetes: it can raise blood sugar - test more often. Vaccines need the doctor's timing. If you become pregnant, call your doctor.
When is it an emergency?
Face or throat swelling, black tarry stools, or sudden severe weakness is urgent care. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What a Pymander AI doctor consult looks like
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Common questions
Why can't I ever stop it suddenly?
Replacement, not treatment: the drug does the adrenal glands' job - stop abruptly and the body has no fallback: weakness, blood-pressure collapse, the Addisonian danger zone. The taper is the doctor's schedule, and the standing rules are unglamorous: never run out, refill early, wear the bracelet, and know your sick-day rules before the sick day arrives.
What are the sick-day rules?
Illness changes the dose: fever, vomiting, diarrhea, injury, or surgery all raise the body's steroid needs - your doctor gives you the personal instruction card in advance: when to adjust, when to call, when to go to the ER. The fridge card and the bracelet are the system; stress dosing without a plan is how Addisonian crises happen. Ask for your card at the next visit if you do not have one.
Why the diet instructions?
The drug moves sodium and potassium: your doctor may set low-sodium, low-salt, potassium-rich, or high-protein instructions - and salt tablets sometimes ride alongside. The diet is part of the prescription, not lifestyle garnish. Muscle weakness, swelling, or a blood-pressure drift is the signal the balance has moved - reportable, not waited out.
Why did my doctor ask about my blood sugar?
Steroids raise it: on fludrocortisone, diabetes management tightens - test more often, and high readings mean the diabetes medication and diet get adjusted. No diabetes? The watch is lighter but the effect is real. The everything-you-take list matters doubly on steroids: interactions are a long column.
Why is a lingering cold a big deal on this drug?
Steroids quiet the immune system: infections smolder instead of flaring - a cold that will not clear, a cut that will not heal, a fever that stays low all get reported early. Vaccines need the doctor's timing. The same immune quieting is why exposures - chickenpox, measles, COVID - get a call rather than a wait-and-see.
What happens if I miss a dose of fludrocortisone?
Take it as soon as you remember, unless it is almost time for the next one - then skip it and never double up. One missed morning usually means a lighter-energy day; the danger is the pattern: two or three missed days in a row on replacement therapy is a call-your-doctor situation, not a catch-up-on-your-own one. The morning anchor - next to the coffee maker - keeps it rare.